The present invention relates to a crystal growing method based on an improved molecular beam epitaxy and single crystal devices fabricated by this method.
In the so-called communications age, the volume of information and data to be exchanged and processed is increasingly growing so that high-capacity and high-speed communication systems and data processing systems have been demanded. To this end, there have been increasingly strong demands for electronic components capable of satisfactorily functioning in SHF band, and optical devices and integrated optical circuits for optical communication and data processing systems. In order to fabricate these electronic and optical components there has been a strong demand for a novel process for growing high quality crystals having multi-dimensional distributions of components and impurity concentration, the distributions being controlled in the order of submicrons.
The conventional selective epitaxy is such that a crystal face of a substrate is masked with a film different chemically and physically from the substrate and having a suitable aperture pattern so that desired crystals may be grown on uncovered regions of the substrate. In order to epitaxially grow crystals having a multi-dimensional structure without the use of a mask, there has been invented and demonstrated a process utilizing a beam of ions, but so far high-quality crystals adapted for the fabrications of electronic devices has not been produced yet because the controls of ion beam convergence, deflection and decleration are difficult and because the atmosphere in a crystal growing container cannot be maintained free from contamination.
In the liquid and gas phase epitaxy based on the thermal equilibrium wherein the crystal growth is effected by the repeated exchanges of atoms and molecules between the surface of crystal growth and a means for supplying these atoms and molecules or materials, it is meaningless to control the direction of incidence of these atoms and molecules on the substrate. However, in the molecular beam and thermal decomposition epitaxy, the material atoms and molecules are transported only in one direction from supply means to a substrate. Therefore when the mean free path (l) of the molecules is made sufficiently longer than the source-to-substrate distance (L), it is possible to control the angles of incidence of epitaxial molecular beams. A solid angle .OMEGA. at a point on a substrate subtended by an aperture with an area S of supply means or beam source is given by EQU .OMEGA.=S/L.sup.2
when l&gt;&gt;L and .OMEGA.=0, a molecular beam from the beam source may be regarded as a parallel beam so that it may be so controlled as to be incident upon the substrate at a predetermined angle. In this molecular beam and thermal decomposition epitaxy wherein the epitaxial growth is effected at a sufficiently reduced pressure, the solid angle .OMEGA. may be made sufficiently small by the geometrical arrangement of a crystal growing apparatus.